The invention is directed to devices for isolating one body from vibration transmitted by another body. In particular, the invention provides a low cost, self-contained, active isolation system that can be readily mounted to an isolation table, or similar structure, to control vibrational disturbances.
Electromagnet actuators are especially well suited for generating forces in situations where the relative displacements are low. Electromagnets are low cost and inexpensive device to operate, which is an additional advantage. Known systems using electromagnets in vibration isolation tables are unduly complicated and lack ease of installation or adjustment. Further, known systems are not readily adaptable for retrofit into an existing isolation table or other structure.
The invention overcomes the deficiencies in the art to provide an isolation system having at least one electromagnet actuator to generate force for canceling vibration in an isolated body (e.g., the table top) transmitted by a supporting body (e.g., the table frame or legs). According to the invention, the system comprises a device having an electromagnet, a motion sensor, and a controller all contained within a single housing that is easily mounted to the isolated body. One or more of the devices can be mounted to the isolated body depending on what modes of vibration are of concern.
Housing the components in a single container or housing facilitates mounting the device to an isolation table, and reduces installation cost and complexity. The housing makes the devices less conspicuous and less intrusive for the user. According to the invention, the housing can be mounted to the table top (which are typically made of a ferrous metal) with permanent magnets, which provides instant attachment and the ability to easily remove and reposition the housing, if desired. Other attachment means, such as adhesives or screw fasteners, could be used as alternatives.
The invention is advantageously installed on an isolation table to act in parallel with a spring system supporting the table on a frame or legs. Such spring systems are typically pneumatic, but the invention can work with other types of spring supports.
According to a preferred embodiment, the sensor is an accelerometer which produces a signal representative of acceleration in the table top. The signal is processed by the controller, which generates a control signal for the electromagnet to cause it to produce a force for canceling the vibration. A preferred control mode is to integrate the acceleration signal to obtain a velocity, and then to feedback a sum of the proportioned acceleration and velocity. Alternatively, another motion sensor could be used with appropriate control. For example, a geophone, velocimeter, or a displacement sensor could be used to sense motion of the table top.
According to one aspect of the invention, a target element is included for the electromagnet to act against with a vibration-canceling force. According to a preferred embodiment, the target element is a permanent magnet. The target element is attached to the supporting frame or legs and the housing is mounted to the table top in proximity to the magnet so that a gap is established between the electromagnet and permanent magnet. The permanent magnet produces a bias that permits the electromagnet to generate a push or a pull force on the permanent magnet, making the vibration canceling forces more effective. Isolation tables typically have horizontal support rails near the table top. For vertical vibration, the target element is conveniently mounted to the rail. For systems without rails between the legs, brackets can be mounted on the legs to provide for a target element. For horizontal vibration, the target element can be mounted to a table leg or bracketry. The housing is appropriately oriented so that the electromagnet is positioned to generate a force acting on the target element across a gap.
According to the invention, the target element alternatively may be a magnetically sensitive element, such as a ferrous metallic member, for which the electromagnet will produce an attractive force. Accordingly, a bias can be applied to the electromagnet by applying a DC input, or by installing a permanent magnet in the electromagnet, so that both attractive and repulsive forces can be generated for effective vibration canceling.
According to another aspect of the invention, the controller includes input and output signal processing. The input processing includes means for trimming any DC bias that might be present thereby adjusting for any DC drift that may result from processing of the input signal. Moreover, at least one, and preferably both, the input and output signal processing may include active gain switching means for switching between a first low gain value to a second higher gain value, preferably by means of a programmable gain amplifier. This provides an adequate strength signal to the control method and/or the actuator for a large range of transmitted vibration levels. Furthermore, one or both of the input and output processing may include means for monitoring the signals for system health monitoring.
The devices according to the invention can include a single electromagnet for single direction vibration control. Alternatively, the device housing can contain two electromagnets relatively oriented for damping in different directions. Sensors are included in the housing for measuring movement in each direction. In addition, target elements are associated with each electromagnet and may, when separate elements, be attached to the table frame at appropriate locations.
A table top is subject to various vibrational disturbances that can cause different movements of the table top, including simple linear vertical vibration, roll movement, pitch movement, longitudinal and lateral horizontal movement, and yaw movement. A system according to the invention includes an isolation table provided with a plurality of devices for controlling these different modes of vibration.
According to one embodiment, a table top is provided with three damping devices for controlling all of the vertical based movements: linear vertical, pitch, and roll vibrations. The devices each include a single electromagnet and associated target permanent magnet. One device is positioned at each of the front two legs of the table, and one device is positioned along the back edge of the table top midway between the back legs. The devices act independently at the various locations and produce damping forces to control the three mentioned vibration movements. The relative spacing and positioning of the active damping units about the table top optimizes the control forces required.
A three-device system advantageously provides vertical vibration control with a minimum number of devices. Alternatively, a table can be provided with four damping devices, one positioned at each table leg, for more robust damping control, i.e., less control force required for each device.
An isolation table can be provided with two devices for control of the two horizontal modes of vibration. The devices are mounted to the table top at adjacent legs with the target elements mounted to, or integral with, each of the legs. Preferably, to position the devices as unobtrusively as possible, the devices are positioned at the back legs. The devices are appropriately aligned to produce a diagonal force vector which passes through the Center of Gravity (CG) of the table. In this way, the longitudinal and lateral movements can be controlled.
According to another embodiment, the devices each include vertically and horizontally oriented electromagnets contained in the single housing, and an isolation table is configured for control of both vertical and horizontal vibration in all six modes. Advantageously, control of all six modes can be achieved with three devices mounted to the table, one each at the front legs and a third at the back edge midway between the back legs. Target elements are positioned on each of the front legs and on the support rails adjacent the front legs. Additionally, a target element is positioned on the rear support rail for vertical control, and a bracket mounted to the rear rail extends vertically upward to support an additional target element for horizontal control by the rear positioned device.
Other configurations are also possible, for example, using multiple damping devices for more robust vibration control. In addition, if a particular form of vibration or movement is a concern, for example, because of the equipment carried on the isolation table, the devices can be positioned accordingly. As one example, for a robot oriented lengthwise on an isolation table, multiple devices can be mounted to the table and oriented for producing horizontal canceling force directed in the longitudinal direction.
Another advantage of the system according to the invention is that having all of the active components in a single housing permits the simple retrofit of existing isolation tables or other structures. In addition, when magnet mountings are used, the damping in an isolation table can be easily adjusted, or even adapted temporarily for a particular use, by adding devices to the table or changing the position or orientation of the devices on the table.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.